Floodlighting applications generally require high power light sources that operate in the the 1000 W to 2000 W power range. Arc discharge lamps that are of the double-ended, unjacketed type are suitable for these applications. Such lamps typically have arc lengths ranging from short (i.e., 30 mm) to long (i.e., 180 mm). However, the type most often utilized for sports lighting application is a jacketed light source (e.g., a BT56 outer bulb). The key to the use of unjacketed arc lamps, such as metal halide systems, resides in the ability to closely couple the lamp to the reflector optics of the fixture in which it will by employed. Benefits of using unjacketed double-ended plasma sources as opposed to jacketed products include high fixture efficiencies and reduction of undesirable stray light.
Prior art lamps with short arc lengths (30 mm range) have been developed for use in such situations; however, such lamps have an elliptical arc chamber in which the quartz is gathered and molded using non-standard manufacturing techniques. See, for example, U.S. Pat. Nos. 5,138,227 and 5,142,195. These lamps are expensive to produce. Additionally, the short arc length can induce spotlight characteristics in some optical systems which can cause poor light blending from fixture to fixture. Further, the small lamp size can place the pinch sealed ends in the optical path of the reflector geometry and thus raise the temperature thereof, leading to premature failures.
Long arc lamps, on the other hand, are not as optically efficient in some luminaires, although, obviously, such disadvantages are functions of the reflector designs.
Also, it has been common in the past to used undoped, clear quartz for the lamp envelopes. Such material passes a good deal of ultra violet (UV) light which can generate ozone in the lamp vicinity. Since ozone is quite reactive, this can lead to deterioration of the fixture and fixture components.